Incognito Keyboard

Signal has a feature called Incognito Keyboard which seems to request to disable personalized learning from user input which some proprietary keyboard apps do. This might be a useful feature for us as well. Signal does it like this:

https://github.com/signalapp/Signal-Android/blob/ba849bce2c90287e820a3008e9dc9a1b14de19fc/src/org/thoughtcrime/securesms/components/ComposeText.java#L154-L156

So it seems to be a quick change.